SiGe tends to oxidize rapidly in air, forming oxides of both Si and Ge. The oxides of Ge tend to be soluble in water. As a result, the near surface region which includes the SiGe is subsequently depleted of Ge. This results in surface roughness that may be a function of the initial Ge concentration. It is therefore desirable to protect the exposed SiGe during general cleaning operations, such as resist strips and post etch cleans.
Processes which utilize an embedded SiGe integration flow typically involve a spacer removal after SiGe growth. The SiGe S/D region(s) should therefore be protected from the severe metallic contamination when, for example, phosphoric acid is used for the spacer removal.
In general, it is known to use thermal protecting oxides to protect surfaces. However, channel stresses derived for the SiGe S/D region(s) will relax if a standard thermal oxidation is performed. This is due to the ease in which the Ge diffuses into a Si substrate. Additionally, the SiGe layer may be substantially oxidized and subsequently removed by the use of thermal oxide as a protecting layer.
Deposited oxides are also often used to protect surfaces. However, in the case of spacer removal, a deposited oxide would prevent the removal of the spacer. Furthermore, deposited oxides tend to suffer from nonuniformity. As a result, they may not provide a feasible screen for extension implants if they also contribute to the spacer thickness and nonuniformity.
Accordingly, there exists a need in the art to overcome the deficiencies and limitations described hereinabove.